AD9520-3 EEPROM settings aren't loaded

Q

We are using an AD9520-3 Clock generator in one of our designs, but unfortunately we are experiencing some problemen with respect to the loading of the eeprom settings, stored inside the AD9520's eeprom memory.We have pulled the eeprom enable input high so it should load from the inside eeprom.If loaded correctly everything works fine, but sometimes, one in 10 startups or so, the eeprom settings aren't loaded and the AD9520 remains configured with it's default settings. This situation is offcource highly unwanted, because the chip doesn't function as expected in such a situation.Strangely enough I'm also able to replicate the problem by invoking a lot of reset pulses on the reset pin, while keeping the chip powered on, then also once in a while the AD9520 doesn't load its eeprom setting. It seems like some form of faulty eeprom loading / reset recognition accurs. What I mean with a lot of reset pulses: we've put a reset button on the PCB, by pressing it you ground the reset input of the AD9520, if you press it really often in a short period of time, we're also able to reproduce the problem, the "fail state" then occurs once in a while. Maybe it has something to do with contact bounce of the reset signal?I would really appreciate any help, I roughly followed the design of the AD9520 evaluation board and studied the datasheet, but I'm not able to see any possible cause of the problem there. There is no mentioning of special reset conditions or circuitry that should be required.

A

The threshold voltage at which the AD9520’s power on reset triggers is a little on the low side if the power supply ramp is slow.

We recommend leaving the RESETb line high during power-up until after the power supplies are stable, and then use a >=20ns low pulse on RESETb.

We’ve had a few other customers with this issue, and this has solved the problem.

Reset button on the PCB: Don’t do that. You can hang the RESET of the part or hang the EEPROM I2C controller.

On other comment: the input clock must be present when the EEPROM is loading, as the VCO calibration depends on an input clock.